title: Asymmetric distribution of carbonic anhydrase in the alveolar-capillary barrier.
abstract: Pulmonary carbonic anhydrase (CA) activity was studied by injecting 0.5 ml of a buffered solution of NaH14CO3 and 3H2O into the distal airways of perfused rabbit lungs. The early recovery of 14C in the pulmonary venous outflow averaged 0.28 +/- 0.02 (SE) that of 3H under control circumstances. Incorporation of a CA inhibitor (20 mg/l acetazolamide) in the perfusate reduced 14C recovery relative to 3H by two-thirds, whereas this inhibitor had no effect when placed in the airway injection fluid. Addition of 100 mg/l Ca to the perfusate did not increase 14C recovery, but addition of the enzyme to the bronchial fluid increased 14C recovery relative to 3H by a factor of more than 5. It is concluded that CA is associated with the endothelial side of the alveolar-capillary barrier but is absent on the airway surfaces.
mesh_terms: D000818:Animals; D001808:Blood Vessels / Q000378:metabolism; D002196:Capillaries / Q000502:physiology*; D002250:Carbon Radioisotopes; D002256:Carbonic Anhydrases / Q000032:analysis*; D008168:Lung / Q000032:analysis*; D010477:Perfusion; D011650:Pulmonary Alveoli / Q000502:physiology*; D011817:Rabbits; D014132:Trachea / Q000378:metabolism; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D014316:Tritium; D002256:Carbonic Anhydrases